This invention relates to the compressive treatment of webs in which a stationary retarding surface acts upon the outer surface of a driven web to cause the web to slow and longitudinally compact or crepe in a treatment zone. This technique, sometimes referred to as bladeless microcreping because of its avoidance of the use of a blade retarder and its ability to produce fine crepes, is exemplified by our prior U.S. Pat. No. 3,810,280, which is herein incorporated by reference.
With this bladeless technique it has been found difficult to obtain the desired level of uniformity of treatment under commercial conditions and at commercial speeds. For example, as speeds have been increased, unwanted non-uniformities have occurred across the width of the web in some cases or in the longitudinal direction, or the characteristics resulting from the treatment have been different over the range of operational speeds. In other cases the characteristics that result from the treatment have been sensitive to slight change in temperature or adjustment, making the technique inappropriate for commercial adoption. In some cases, prior implementations of the bladeless technique have caused snagging or surface abrasion or other harm to the web.
For such reasons the commercial use of this technique has been limited, despite its potential advantages and the importance of the possible fields of application. An example of an important field is that of denim fabrics, in which mechanical treatment by the technique, if perfected, has wide potential. Another example is the field of specialty fabrics, where mechanical treatment is desired for giving to rather inexpensive or low quality fabrics, characteristics that enhance their value and quality.
The bladeless technique is applicable to compaction of webs in which components of the web, e.g. a knit or woven material, are longitudinally compacted with extreme uniformity and without introduction of crepe, and to various degrees of creping, from the finest microcrepe to rather gross crepe, or combinations of primary and secondary crepes or decorative effects. In some cases tension is applied to the treated web to remove some or even most of the treatment, e.g. where it is desired mainly to soften the web or render it pliable. In addition to textile fabrics the technique is applicable to a wide range of nonwoven fabrics, papers and other web-form flexible sheets and the like.
Various aspects of the present invention are believed to meet, in a commercially practical manner, the needs mentioned above as well as others that are encountered in the longitudinal compressive treatment of webs.
Certain aspects of the invention are applicable to other web treatment machines besides the bladeless microcreper.